Two new polls found former Gov. Angus King (I) leading his Democratic and Republican competitors, but by a smaller margin than he was before the U.S. Chamber of Commerce and the National Republican Senatorial Committee launched attack ads to undermine his Senate candidacy.

Both polls were done using robocalls to landlines only, a polling strategy that is not considered as accurate as using live interviewers to call cellphones and landlines. Still, the new data offer a revealing view into a race that is thought to be King’s to lose.

The nonpartisan Maine People’s Resource Center found King leading Summers by 16 points among registered voters. King took 44 percent to Summers’ 28 percent and Dill’s 15 percent.

King, a former two-term governor of the Pine Tree State, is widely expected to caucus with Democrats if he becomes Maine’s new Senator.

In a mid-June poll conducted by the MassINC Polling Group for WBUR, which used live telephone interviewers to interview likely voters, King took 50 percent to Summers’ 23 percent. Dill took only 9 percent.

“$1.7 million of negative advertising by out-of-state partisan interests has worked to some degree,” admitted King’s communications director, Crystal Canney. “But the mistruth in those ads is disgusting.”

She said the campaign isn’t taking its lead in recent polling for granted and that King is out there working hard.

If GOP interests can pull Dill’s numbers up significantly, there’s a path, if narrow, for Summers to squeak out a victory.

Right now, though, Roll Call continues to rate this race as Likely Independent.

The PPP poll was conducted from Sept. 17-18 among 804 likely voters and had a margin of error of 3.5 points. The MPRC poll was conducted Sept. 15-17 among 856 registered voters and had a margin of error of 3.4 points. The MassINC poll was conducted June 13-14 among 506 likely voters and had a margin of error of 4.4 points.